Multi-image display apparatus providing holographic image

ABSTRACT

Provided is a multi-image display apparatus including a light source configured to emit light, a spatial light modulator configured to provide a first image by modulating the light emitted from the light source, and an optical system configured to transmit the first image provided by the spatial light modulator to a viewer, wherein the optical system is configured such that a travelling path of the first image provided by the spatial light modulator includes a first optical path in a first direction, a second optical path in a second direction orthogonal to the first direction, and a third optical path in a third direction orthogonal to the first direction and the second direction, respectively, and wherein the optical system is configured such that the first image and a second image provided from an optical path different from the travelling path of the first image are provided to the viewer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority from Korean Patent Application No.10-2019-0053889, filed on May 8, 2019, and Korean Patent Application No.10-2019-0083944, filed on Jul. 11, 2019, in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein intheir entireties by reference.

BACKGROUND 1. Field

Example embodiments of the present disclosure relate to multi-imagedisplay apparatuses, for example, an augmented reality (AR) system, andmore particularly, to multi-image display apparatuses capable ofproviding a holographic image.

2. Description of the Related Art

Along with the recent development of electronic devices and displayapparatuses capable of implementing virtual reality (VR), interest in VRis also increasing. Techniques capable of implementing augmented reality(AR) and mixed reality (MR) as the next stage of VR have been studied.

AR, unlike VR assuming a complete virtual world, is a display technologyfor showing a virtual object or information in an overlapping (orcombined) manner in a real-world environment, further enhancing theeffect of reality. While VR is only applicable to the field of games orvirtual experiences, AR is applicable to various real environments. Inparticular, AR draws the attention as a next generation displaytechnology suitable for a ubiquitous environment or an internet ofthings (IoT) environment. Such AR may be an example of MR in that itshows the real world and additional information such as the virtualworld in a mixed manner.

SUMMARY

One or more example embodiments provide multi-image display apparatuses,for example, an augmented reality (AR) system, and more particularly, tomulti-image display apparatuses capable of providing a holographicimage.

According to an aspect of an example embodiment, there is provided amulti-image display apparatus including a light source configured toemit light, a spatial light modulator configured to provide a firstimage by modulating the light emitted from the light source, and anoptical system configured to transmit the first image provided by thespatial light modulator to a viewer, wherein the optical system isconfigured such that a first travelling path of the first image providedby the spatial light modulator includes a first optical path in a firstdirection, a second optical path in a second direction orthogonal to thefirst direction, and a third optical path in a third directionorthogonal to the first direction and the second direction, and whereinthe optical system is configured such that the first image and a secondimage provided from a second travelling path that is different from thefirst travelling path are provided to the viewer along the third opticalpath.

The first image may be a virtual holographic image and the second imagemay be an external image including an actual external scene.

The spatial light modulator may include a reflective spatial lightmodulator configured to reflect and modulate the light emitted from thelight source.

The optical system may include a first beam splitter configured toreflect the light emitted from the light source to the spatial lightmodulator and transmit the light reflected from the spatial lightmodulator, a second beam splitter configured to transmit the light fromthe first beam splitter, a first mirror configured to reflect the lighttransmitted through the second beam splitter towards the second beamsplitter, a third beam splitter provided in the second direction fromthe second beam splitter, and a second mirror configured to reflectlight from the third beam splitter towards the third beam splitter.

The second beam splitter may be configured to reflect the lightreflected from the first mirror towards the third beam splitter.

Each of the first beam splitter, the second beam splitter, and the thirdbeam splitter may include a semi-transmissive mirror configured toreflect half of the incident light and transmit the other half of theincident light.

Each of the first beam splitter, the second beam splitter, and the thirdbeam splitter may include a polarization beam splitter configured toreflect light having a first linearly polarized light component andtransmit light having a second linearly polarized light component thatis orthogonal to the first linearly polarized light component.

The optical system may further include a first quarter-wave plateprovided between the second beam splitter and the first mirror, and asecond quarter-wave plate provided between the third beam splitter andthe second mirror.

The third beam splitter may be configured to reflect the light from thesecond beam splitter and transmit the light reflected from the secondmirror.

The second mirror may include a first surface facing the third beamsplitter and a second surface opposite to the first surface, and thesecond mirror may be configured to reflect a first image incident on thefirst surface and to transmit a second image incident on the secondsurface.

Each of the first beam splitter and the second beam splitter may includea polarization beam splitter configured to reflect light having a firstlinearly polarized light component and transmit light having a secondlinearly polarized light component that is orthogonal to the firstlinearly polarized light component, and the third beam splitter mayinclude a polarization beam splitter configured to transmit light havinga first linearly polarized light component and reflect light having asecond linearly polarized light component orthogonal to the firstlinearly polarized light component.

The third beam splitter may be configured to transmit the light from thesecond beam splitter and to reflect the light reflected from the secondmirror.

The optical system may further include a first lens provided between thespatial light modulator and the first beam splitter, a second lensprovided between the first beam splitter and the second beam splitter,and a third lens provided between the second beam splitter and the thirdbeam splitter.

Each of the first lens and the second lens may include a convex lens,and the third lens may include a concave lens.

The optical system may further include a spatial filter provided betweenthe first beam splitter and the second beam splitter proximate to afocal point of the first lens.

The first optical path may be provided between the spatial lightmodulator and the first mirror, a second optical path may be providedbetween the second beam splitter and the third beam splitter, and athird optical path may be provided between the second mirror and aviewer.

The first optical path and the third optical path may have differentpositions in the second direction, and the second optical path may bevertically provided between the first optical path and the third opticalpath in the second direction.

At least one of the first mirror and the second mirror may include aconcave mirror.

The second mirror may include a concave mirror, and the optical systemmay be configured to form a real image of the first image between afocal point of the second mirror and the second mirror.

At least one of the first mirror and the second mirror may include aconcave mirror.

The optical system may include a first beam splitter configured toreflect the light emitted from the light source towards the spatiallight modulator and to transmit the light reflected from the spatiallight modulator, a first mirror configured to reflect the light from thefirst beam splitter, a second beam splitter provided in the seconddirection from the first mirror, and a second mirror configured toreflect the light from the second beam splitter towards the second beamsplitter.

The second beam splitter may be configured to reflect the light from thefirst mirror and to transmit the light reflected from the second mirror.

Each of the first beam splitter and the second beam splitter may includea polarization beam splitter configured to reflect light having a firstlinearly polarized light component and to transmit light having a secondlinearly polarized light component that is orthogonal to the firstlinearly polarized light component, and the optical system may furtherinclude a half-wave plate provided between the first beam splitter andthe second beam splitter, and a quarter-wave plate provided between thesecond beam splitter and the second mirror.

The first beam splitter may include a polarization beam splitterconfigured to reflect light having a first linearly polarized lightcomponent and to transmit light having a second linearly polarized lightcomponent that is orthogonal to the first linearly polarized lightcomponent, and the second beam splitter may include a polarization beamsplitter configured to transmit light having a first linearly polarizedlight component and to reflect light having a second linearly polarizedlight component, and the optical system may further include aquarter-wave plate provided between the second beam splitter and thesecond mirror.

The second beam splitter may be configured to transmit light from thefirst mirror and to reflect light reflected from the second mirror.

The spatial light modulator may include a transmissive spatial lightmodulator configured to transmit and modulate the light emitted from thelight source.

The optical system may include a second beam splitter configured totransmit the light provided from the spatial light modulator, a firstmirror configured to reflect the light transmitted through the secondbeam splitter towards the second beam splitter, a third beam splitterprovided in the second direction from the second beam splitter, and asecond mirror configured to reflect the light from the third beamsplitter towards the third beam splitter.

The optical system may further include a first lens and a second lensprovided between the spatial light modulator and the second beamsplitter, a spatial filter provided between the first lens and thesecond lens, and a third lens provided between the second beam splitterand the third beam splitter.

Each of the first lens and the second lens may include a convex lens,and the third lens may include a concave lens.

The first optical path may be provided between the light source and thefirst mirror, the second optical path may be provided between the secondbeam splitter and the third beam splitter, and the third optical pathmay be provided between the second mirror and the viewer

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects, features, and advantages of exampleembodiments will be more apparent from the following description takenin conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view illustrating a configuration of amulti-image display apparatus according to an example embodiment;

FIG. 2 is a cross-sectional view taken along a direction illustrating anarrangement of some components of the multi-image display apparatus ofFIG. 1;

FIG. 3 is a cross-sectional view taken along another directionillustrating an arrangement of some other components of the multi-imagedisplay apparatus of FIG. 1;

FIG. 4 is a diagram of a configuration in still another direction of themulti-image display apparatus of FIG. 1;

FIGS. 5 and 6 are diagrams showing a principle of controlling a depth ofa holographic image seen by a viewer in the multi-image displayapparatus of FIG. 1;

FIG. 7 is a graph showing a relationship between the location change ofan image formed around a spatial light modulator and a depth of aholographic image seen by a viewer;

FIG. 8 is a block diagram of a configuration of a multi-image displayapparatus according to an example embodiment;

FIG. 9 is a diagram illustrating an arrangement of some components amongcomponents of a multi-image display apparatus according to an exampleembodiment;

FIG. 10 is a cross-sectional view illustrating an arrangement of somecomponents of a multi-image display apparatus according to an exampleembodiment;

FIG. 11 is a sectional view illustrating an arrangement of somecomponents of a multi-image display apparatus according to an exampleembodiment;

FIG. 12 is a cross-sectional view illustrating an arrangement of somecomponents of a multi-image display apparatus according to an exampleembodiment;

FIG. 13 is a cross-sectional view of an example arrangement of somecomponents of a multi-image display apparatus according to an exampleembodiment;

FIG. 14 is a cross-sectional view illustrating an arrangement of somecomponents of a multi-image display apparatus according to an exampleembodiment;

FIG. 15 is a schematic perspective view illustrating a configuration ofa multi-image display apparatus according to an example embodiment;

FIG. 16 is a cross-sectional view taken along a direction illustratingan arrangement of some components of the multi-image display apparatusof FIG. 15;

FIG. 17 is a cross-sectional view taken along a direction illustratingan arrangement of some components of the multi-image display apparatusof FIG. 15;

FIG. 18 is a cross-sectional view taken along another directionillustrating an arrangement of some other components of the multi-imagedisplay apparatus of FIG. 15; and

FIGS. 19, 20, and 21 show various electronic devices employing amulti-image display apparatus according to example embodiments.

DETAILED DESCRIPTION

Hereafter, a multi-image display apparatus according to exampleembodiments will be described more fully with reference to theaccompanying drawings. In the drawings, like reference numerals refer tolike elements and a size of each element may be exaggerated for clarityand convenience of a description. Also, the following exampleembodiments described below are merely illustrative, and variousmodifications may be possible from the example embodiments. Also, in alayer structure described below, when a position of an element isdescribed using an expression “above” or “on”, the position of theelement may include not only the element being “immediatelyon/under/left/right in a contact manner” but also being“on/under/left/right in a non-contact manner”.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. In addition, unlessexplicitly described to the contrary, the word “include,” “comprise” andvariations such as “includes,” “comprises” or “comprising” will beunderstood to imply the inclusion of stated elements but not theexclusion of any other elements. Expressions such as “at least one of,”when preceding a list of elements, modify the entire list of elementsand do not modify the individual elements of the list. For example, theexpression, “at least one of a, b, and c,” should be understood asincluding only a, only b, only c, both a and b, both a and c, both b andc, or all of a, b, and c.

FIG. 1 is a perspective view showing a configuration of a multi-imagedisplay apparatus 100 according to an example embodiment. Referring toFIG. 1, the multi-image display apparatus 100 according to an exampleembodiment may include a light source 110, an optical system 120, and aspatial light modulator 130.

The light source 110 may be a coherent light source that emits coherentlight. In order to provide light having high coherency, for example, alaser diode (LD) may be used as the light source 110. Also, the lightsource 110 may include a light-emitting diode (LED). An LED has lowerspatial coherence than a laser, but light may be sufficiently diffractedand modulated by the spatial light modulator 130 as long as the lighthas a certain degree of spatial coherence. However the light source 110is not limited thereto, and any other light source that may emit lighthaving spatial coherence may be used as the light source 110.

Also, in the example embodiment shown in FIG. 1, the light source 110may include a point light source that emits diverging light. A pointlight source, such as an LED or an LD, may be directly disposed at thelocation of the light source 110 shown in FIG. 1, but the point lightsource may be disposed on another location for convenience of design andlight may be transmitted through an optical fiber. For example, anoptical fiber end may be disposed at the location of the light source110 depicted in FIG. 1. Also, in FIG. 1, the light source 110 isdepicted as one component, but the light source 110 may include aplurality of LDs or LEDs that provide red, green, and blue light,respectively.

The spatial light modulator 130 may form a hologram pattern according toa hologram data signal, for example, a computer generated hologram (CGH)signal provided from an image processing apparatus. As a result of thediffraction of incident light emitted from the light source 110 andincident on the spatial light modulator 130 by the hologram patternformed in the spatial light modulator 130, a holographic image having athree-dimensional effect may be reproduced. The spatial light modulator130 may be one of a phase modulator capable of only performing phasemodulation, an amplitude modulator capable of only performing amplitudemodulation, and a complex modulator capable of performing both phasemodulation and amplitude modulation. In FIG. 1, the spatial lightmodulator 130 may include a reflective spatial light modulator thatdiffracts and modulates incident light while reflecting light. Forexample, the spatial light modulator 130 may include a liquid crystal onsilicon (LCoS), a digital micromirror device (DMD), or a semiconductormodulator.

The optical system 120 transmits a holographic image formed around thespatial light modulator 130 to the viewer's eyes. Also, the opticalsystem 120 may be configured to transmit an external scene to theviewer's eye together with the holographic image. The characteristics ofthe multi-image display apparatus 100, such as a viewing angle of aholographic image, an image quality of an image, the size of themulti-image display apparatus 100, etc. may vary according to the designof the optical system 120.

In the example embodiment depicted in FIG. 1, the optical system 120includes a first beam splitter 121 and a second beam splitter 124 facingeach other, a first mirror 126 that reflects light transmitted throughthe second beam splitter 124, a third beam splitter 128 disposed belowthe second beam splitter 124, and a second mirror 129 that re-reflectsthe light reflected from the third beam splitter 128.

The first beam splitter 121 may be disposed so that two differentsurfaces of the first beam splitter 121 face the light source 110 andthe spatial light modulator 130, respectively. For example, the lightsource 110 may be disposed in a +z direction with respect to the firstbeam splitter 121, and the spatial light modulator 130 may be disposedin a −y direction with respect to the first beam splitter 121. The firstbeam splitter 121 may be configured to reflect light emitted from thelight source 110 to the spatial light modulator 130 and to transmit thelight reflected from the spatial light modulator 130 to the second beamsplitter 124. Accordingly, the light reflected from the spatial lightmodulator 130 may pass through the first beam splitter 121 and travel ina +y direction toward the second beam splitter 124.

The second beam splitter 124 and the first mirror 126 may besequentially disposed in the +y direction away from the first beamsplitter 121. The second beam splitter 124 may be configured to transmitlight reflected from the spatial light modulator 130 and to reflect thelight reflected from the first mirror 126 in a −z direction, that is,downward in FIG. 1. Accordingly, light reflected by the spatial lightmodulator 130 may reach the first mirror 126 after passing through thefirst beam splitter 121 and the second beam splitter 124. Afterwards,the light is reflected by the first mirror 126, the light isre-reflected by the second beam splitter 124, and enters the third beamsplitter 128.

The third beam splitter 128 may be disposed to face the second beamsplitter 124 in the −z direction. Also, the second mirror 129 may bedisposed to face the third beam splitter 128 in an −x direction. Thethird beam splitter 128 may be configured to reflect light reflectedfrom the second beam splitter 124 to the second mirror 129 and totransmit the light reflected from the second mirror 129. In this way,light reflected from the second mirror 129 may reach the viewer's eyesafter transmitting through the third beam splitter 128. Also, the secondmirror 129 may be configured to transmit light traveling in a +xdirection from the outside. Then, a viewer's eyes may see an externalscene through the second mirror 129.

The first beam splitter 121, the second beam splitter 124, and the thirdbeam splitter 128 may include semi-transmissive mirrors that simplyreflect half of incident light and transmit the other half. When thefirst beam splitter 121, the second beam splitter 124, and the thirdbeam splitter 128 include semi-transmissive mirrors, the first quarterwave plate 125 a and the second quarter wave plate 125 b described belowmay be omitted from the optical system 120. To use light moreefficiently, the first beam splitter 121, the second beam splitter 124,and the third beam splitter 128 may include polarization beam splittersthat transmit or reflect incident light according to the polarizationstate of incident light.

FIG. 2 is a cross-sectional view taken along a direction illustrating anarrangement of some of the components of the multi-image displayapparatus 100 of FIG. 1. For example, FIG. 2 is a cross-sectional viewof the optical system 120 with a plane including a z-axis and a y-axisto show the components from the spatial light modulator 130 disposed inthe +y direction to the first mirror 126.

Referring to FIG. 2, the light source 110 is disposed to face a firstsurface 121 a of the first beam splitter 121. Accordingly, light emittedfrom the light source 110 is incident on the first surface 121 a of thefirst beam splitter 121. The first beam splitter 121 may be apolarization beam splitter that reflects light having a first linearlypolarized light component and transmits light having a second linearlypolarized light component orthogonal to the first linearly polarizedlight component. In this case, of light emitted from the light source110, light having the first linearly polarized light component isreflected by the first beam splitter 121 and light having the secondlinearly polarized light component may be transmitted through the firstbeam splitter 121.

The light having the first linearly polarized light component reflectedby the first beam splitter 121 is emitted through a second surface 121 bof the first beam splitter 121 and enters the spatial light modulator130. The spatial light modulator 130 is disposed facing the secondsurface 121 b of the first beam splitter 121. Also, the optical system120 may further include a first lens 122 a between the second surface121 b of the first beam splitter 121 and the spatial light modulator130. Light emitted from the light source 110 may be a diverging beam inwhich a beam diameter gradually increases in a traveling direction oflight. The first lens 122 a may make light incident from the first beamsplitter 121 parallel light having a constant beam diameter. For thisreason, the first lens 122 a may be a convex lens. Accordingly, theparallel light having a constant beam diameter enters the spatial lightmodulator 130.

The spatial light modulator 130 modulates and reflects incident light,and the modulated light interferes with each other to form a holographicimage. Then, when the light is modulated by the spatial light modulator130, the light is rotated 90 degrees and has the second linearlypolarized light component. In this way, the light including theholographic image re-enters the second surface 121 b of the first beamsplitter 121. At this point, the light is focused while passing throughthe first lens 122 a. Accordingly, the beam diameter of the light isgradually reduced in a traveling direction of light. Light having thesecond linearly polarized light component is transmitted through thefirst beam splitter 121 and is emitted through a third surface 121 c ofthe first beam splitter 121 facing the second surface 121 b. Thus, thelight may enter a first surface 124 a of the second beam splitter 124.

The optical system 120 may further include a spatial filter 123 and asecond lens 122 b disposed on an optical path between the first beamsplitter 121 and the second beam splitter 124. The spatial filter 123removes unnecessary light components other than the holographic image.The spatial filter 123 and the second lens 122 b may be disposed near afocal point of the first lens 122 a. In FIG. 2, the spatial filter 123is disposed ahead in the traveling direction of light, and the secondlens 122 b is disposed behind the spatial filter 123, but embodimentsare not limited thereto. For example, the second lens 122 b may bedisposed ahead in the traveling direction of light, and the spatialfilter 123 may be disposed behind the second lens 122 b.

Light focused by the first lens 122 a becomes a divergent beam in whicha beam diameter is gradually increased again as it passes through thefocal point of the first lens 122 a, but the second lens 122 b maysuppress the beam diameter of light entering the first surface 124 a ofthe second beam splitter 124 not to be excessively increased. Forexample, the second lens 122 b may make light incident on the firstsurface 124 a of the second beam splitter 124 parallel light or adivergent beam with a slowly increasing beam diameter. For this reason,the second lens 122 b may be a convex lens.

The second beam splitter 124 is a polarization beam splitter thatreflects light having a first linearly polarized light component andtransmits light having a second linearly polarized light componentorthogonal to the first linearly polarized light component. Accordingly,light of the second linearly polarized light component incident on thefirst surface 124 a of the second beam splitter 124 from the first beamsplitter 121 is transmitted through the second beam splitter 124 and isemitted through the second surface 124 b facing the first surface 124 aof the second beam splitter 124. The first mirror 126 is disposed facingthe second surface 124 b of the second beam splitter 124. Accordingly,light emitted through the second surface 124 b of the second beamsplitter 124 may enter the first mirror 126.

The optical system 120 may further include a first quarter-wave plate125 a disposed on an optical path between the second surface 124 b ofthe second beam splitter 124 and the first mirror 126. The firstquarter-wave plate 125 a delays incident light by a quarter wavelengthof the incident light. Accordingly, light having a first linearlypolarized light component is converted into light having a firstcircularly polarized light component by the first quarter-wave plate 125a, and light having the first circularly polarized light component isconverted into light having the first linearly polarized light componentby the first quarter wave plate 125 a. Also, light having a secondlinearly polarized light component is converted into light having asecond circularly polarized light component by the first quarter-waveplate 125 a, and light having the second circularly polarized lightcomponent is converted into light having the second linearly polarizedlight component by the first quarter-wave plate 125 a.

Light emitted through the second surface 124 b of the second beamsplitter 124 has a second circularly polarized light component whilepassing through the first quarter-wave plate 125 a. Light having asecond circularly polarized light component is reflected in an oppositedirection, that is, in a direction of 180 degrees with respect to theincidence direction by the first mirror 126. At this time, the polarizedcomponent of the light reflected by the first mirror 126 is convertedinto a first circularly polarized light component. Then, the light mayhave a first linearly polarized light component while passing throughthe first quarter-wave plate 125 a again. Afterwards, light having thefirst linearly polarized light component enters the second surface 124 bof the second beam splitter 124 and is reflected by the second beamsplitter 124.

The light reflected by the second beam splitter 124 is emitted through athird surface 124 c of the second beam splitter 124. The optical system120 may further include a third lens 127 disposed to face the thirdsurface 124 c of the second beam splitter 124. According to the exampleembodiment, the first mirror 126 may be a concave mirror having aconcave reflecting surface. Accordingly, the first mirror 126 may makethe reflected light into a converging beam in which a beam diameter isgradually reduced in a traveling direction of light. The third lens 127converts the converging beam back into a diverging beam to increase aviewing angle of the holographic image seen by the viewer. For thisreason, the third lens 127 may be a concave lens.

FIG. 3 is a cross-sectional view taken along another directionillustrating an arrangement of some other components of the multi-imagedisplay apparatus 100 of FIG. 1. For example, FIG. 3 is across-sectional view of the optical system 120 taken along a planeincluding the z-axis and the x-axis in FIG. 1 to specifically show apath of light from the second beam splitter 124 to the viewer's eyes.The cross-sectional view of FIG. 3 is rotated by 90 degrees with respectto the cross-sectional view of FIG. 2, and thus, in FIG. 3, a linearlypolarized light component is displayed in reverse to FIG. 2. Forexample, although the first linearly polarized light component isrepresented by ‘⊙’ and the second linearly polarized light component by‘

’ in FIG. 2, in FIG. 3, the first linearly polarized light component isrepresented by ‘

’ and ‘↔’ and the second linearly polarized light component isrepresented by ‘⊙’.

Referring to FIG. 3, light of the first linearly polarized lightcomponent reflected by the second beam splitter 124 and passing throughthe third lens 127 enters the third beam splitter 128. Like the firstand second beam splitters 121 and 124, the third beam splitter 128 is apolarized light beam splitter that reflects light having the firstlinearly polarized light component and transmits light having the secondlinearly polarized light component orthogonal to the first linearlypolarized light component. In FIG. 2, the first beam splitter 121 andthe second beam splitter 124 are shown as a cube, and in FIG. 3, thethird beam splitter 128 is shown as a flat plate, but the presentembodiment is not limited thereto. The first beam splitter 121, thesecond beam splitter 124, and the third beam splitter 128 may beselected in a cube shape or a flat plate shape depending on the needs ofthe assembly process of the optical system 120.

Light of the first linearly polarized light component reflected by thethird beam splitter 128 enters the second mirror 129. The optical system120 may further include a second quarter-wave plate 125 b disposed on anoptical path between the third beam splitter 128 and the second mirror129. Accordingly, light of the first linearly polarized light componentis converted into light of the first circularly polarized lightcomponent while passing through the second quarter-wave plate 125 b. Thelight having the first circularly polarized light component is reflectedin the opposite direction, that is, in a direction of 180 degrees withrespect to an incidence direction by the second mirror 129. At thistime, the polarized light component of the light reflected by the secondmirror 129 is converted into the second circularly polarized lightcomponent. Then, the light has a second linearly polarized lightcomponent while passing through the second quarter-wave plate 125 bagain. Afterwards, the light having the second linearly polarized lightcomponent is transmitted through the third beam splitter 128 to enter aviewer's eye E. According to the example embodiment, the second mirror129 may be a concave mirror having a concave reflecting surface forconverging reflected light. Accordingly, a holographic image IMG1 can beprovided to a pupil of the viewer's eye E through the second mirror 129.

The second mirror 129 may also be a semi-transmissive mirror thattransmits a portion of incident light and reflects a remaining portionof the incident light. Then, light including an external scene may betransmitted through the second mirror 129 and the third beam splitter128 and may enter the viewer's eye E as an external image IMG2. Forexample, the second mirror 129 includes a first surface S1 facing thethird beam splitter 128 and a second surface S2 facing the first surfaceS1 and may reflect the holographic image IMG1 incident on the firstsurface S1 and transmit the external image IMG2 incident on the secondsurface S2.

Instead, the second mirror 129 may be a polarization-selective mirrorthat reflects light having a first circularly polarized light componentand transmits light having a second circularly polarized lightcomponent. In this case, light of the first circularly polarized lightcomponent including the holographic image IMG1 is reflected by the firstsurface S1 of the second mirror 129. On the other hand, of lightincluding the external image IMG2, the light of the second circularlypolarized light component passes through the second surface S2 of thesecond mirror 129, and afterwards, may have a second linearly polarizedlight component while passing through the second quarter-wave plate 125b. Afterwards, light including the external image IMG2 converted intothe second linearly polarized light component may enter the viewer's eyeE through the third beam splitter 128.

Instead, the second mirror 129 may be configured to reflect lightincident on the first surface S1 and transmit light incident on thesecond surface S2. In this case, the light including the external imageIMG2 that entered the second surface S2 of the second mirror 129 entersthe third beam splitter 128 after passing through the second mirror 129and the second quarter wave-plate 125 b. Of the light including theexternal image IMG2, light having the second linearly polarized lightcomponent may enter the viewer's eye E through the third beam splitter128.

As described with reference to FIGS. 2 and 3, the optical system 120 mayinclude an optical path having three different directions. For example,the optical system 120 may include a first optical path in a y-directionbetween the spatial light modulator 130 and the first mirror 126, asecond optical path in a z-direction between the second beam splitter124 and the third beam splitter 128, and a third optical path in anx-direction between the second mirror 129 and the viewer. The directionof the first optical path, the direction of the second optical path, andthe direction of the third optical path are orthogonal to each other.Also, the first optical path, the second optical path, and the thirdoptical path have different positions in a height direction. Forexample, the third optical path is located at a lower position than thefirst optical path, and the second optical path is vertically formedbetween the first optical path and the third optical path. Through thearrangement of the optical paths described above, a form factor of themulti-image display apparatus 100 may be formed to be relatively small.Finally, the holographic image IMG1 and the external image IMG2 may beprovided to the viewer's eye E along the third optical path.

According to the example embodiment, the holographic image IMG1reproduced by the spatial light modulator 130 and the external imageIMG2 including the actual external scene may be simultaneously providedto the viewer's eye. Then, the user may view the holographic image IMG1including virtual reality or virtual information together with abackground subject of the real world that the user is actually facing.Accordingly, the multi-image display apparatus 100 according to theexample embodiment may be applied to realize augmented reality (AR) ormixed reality (MR). In this case, the multi-image display apparatus 100according to the example embodiment may be a near-eye AR displayapparatus.

Also, FIG. 4 is a diagram of the configuration in still anotherdirection of the multi-image display apparatus 100 depicted in FIG. 1.For example, FIG. 4 shows the multi-image display apparatus 100 of FIG.1 viewed from the top in the −z-axis direction, and some configurationsare shown in cross-section shapes. The direction depicted in FIG. 4 isrotated by 90 degrees with respect to the direction depicted in FIG. 2,and thus, the linearly polarized light component in FIG. 4 is displayedin reverse to FIG. 2. For example, in FIG. 2, the first linearlypolarized light component is represented by ‘⊙’ and the second linearlypolarized light component is represented by ‘

’, but in FIG. 4, the first linearly polarized light component isrepresented by ‘

’ and the second linearly polarized light component is represented by‘⊙’.

Referring to FIG. 4, the light source 110 may face an upper surface ofthe first beam splitter 121, that is, the center of the first surface121 a. As described above, light emitted from the light source 110 mayenter a viewer's eye and may pass through the first beam splitter 121,the first lens 122 a, the spatial light modulator 130, the first lens122 a, the first beam splitter 121, the spatial filter 123, the secondlens 122 b, the second beam splitter 124, the first quarter-wave plate125 a, the first mirror 126, the first quarter-wave plate 125 a, thesecond beam splitter 124, the third lens 127 (refer to FIGS. 2 and 3),the third beam splitter 128 (refer to FIG. 3), the second quarter-waveplate 125 b, the second mirror 129, the second quarter-wave plate 125 b,and the third beam splitter 128.

Here, the spatial light modulator 130, the first lens 122 a, the firstbeam splitter 121, the spatial filter 123, the second lens 122 b, thesecond beam splitter 124, the first quarter-wave plate 125 a, and thefirst mirror 126 may be disposed in a row on the same layer. The lightsource 110 is disposed above the first beam splitter 121 and the thirdlens 127 is disposed below the second beam splitter 124. The third beamsplitter 128, the second quarter-wave plate 125 b, and the second mirror129 may be disposed in a row on the same layer below the third lens 127.In particular, the third beam splitter 128, the second quarter-waveplate 125 b, and the second mirror 129 may be disposed on the same layeras the viewer's eye E. Also, a direction in which the spatial lightmodulator 130, the first lens 122 a, the first beam splitter 121, thespatial filter 123, the second lens 122 b, the second beam splitter 124,the first quarter-wave plate 125 a, and the first mirror 126 aredisposed is orthogonal to a direction in which the third beam splitter128, the second quarter-wave plate 125 b, and the second mirror 129 aredisposed. For example, in FIG. 1, light travels from the spatial lightmodulator 130 to the first mirror 126 in the y direction, and lightbetween the third beam splitter 128 and the second mirror 129 travels inthe x direction.

Since the multi-image display apparatus 100 according to the exampleembodiment provides a three-dimensional holographic image together withan actual external scene, the multi-image display apparatus 100 mayprovide a more realistic augmented reality experience. Also, themulti-image display apparatus 100 according to the example embodimentdescribed above may increase a length of an optical path in a narrowspace by using the first beam splitter 121, the second beam splitter124, and the third beam splitter 128, and thus, may have a relativelysmall form factor, thereby reducing the size thereof. Accordingly, thevolume and weight of the multi-image display apparatus 100 may bereduced, thereby enhancing convenience for the user. Also, themulti-image display apparatus 100 according to the example embodimentdescribed above may realize a relatively wide viewing angle of about 60degrees.

For example, FIGS. 5 and 6 are diagrams showing a principle ofcontrolling a depth of a holographic image seen by a viewer in themulti-image display apparatus 100 of FIG. 1. In FIG. 5, f represents afocal point of the second mirror 129. When parallel light enters thesecond mirror 129, the light reflected by the second mirror 129 iscollected at the focal point f. However, since the light diverged by thethird lens 127, which is a concave lens, enters the second mirror 129,light may be focused on the viewer's eye E, which is located fartherfrom the second mirror 129 than the focal point f. Meanwhile, a realimage may be formed between the second mirror 129 and the focal point fby controlling the refractive powers of the optical components, such asthe first lens 122 a, the second lens 122 b, the first mirror 126, andthe third lens 127. Then, an enlarged virtual image formed at a distanceD from the viewer is seen by the viewer's eye E. Accordingly, themulti-image display apparatus 100 may realize a relatively wide viewingangle.

A depth of the reproduced holographic image, that is, the distance D,may be controlled by the location of an actual image formed around thespatial light modulator 130. Referring to FIG. 6, a hologram data signalprovided from an image processing apparatus to the spatial lightmodulator 130 includes depth information of a holographic image to bereproduced. The location of the holographic plane of the image formedaround the spatial light modulator 130 is changed according to the depthinformation. Then, the location of an actual image relayed by theoptical system 120 on the optical path between the second mirror 129 andthe focal point f thereof from a holographic plane is changed, and as aresult, a distance by which an enlarged virtual image is viewed by theviewer is changed.

For example, when the location of the holographic plane coincides withthe location of the spatial light modulator 130 as indicated by ‘A’, thelocation of the holographic plane may be defined as 0 (zero). Also, whenthe holographic plane is located in a direction in which light travelsfrom a reflection surface of the spatial light modulator 130 asindicated by ‘B’, it may be defined that the location value of theholographic plane has a positive sign (+). Also, when the holographicplane is located in a direction opposite to the direction in which lighttravels from the reflection surface of the spatial light modulator 130as indicated by ‘C’, it may be defined that the location value of theholographic plane has a negative sign (−).

FIG. 7 is a graph showing an example relationship between the locationchange of an image formed around the spatial light modulator 130 and adepth of a holographic image seen by a viewer. Referring to FIG. 7, asthe location value of the holographic plane increases in the positive(+) direction, that is, as the holographic plane moves away from thereflection surface of the spatial light modulator 130 in a direction inwhich light travels, the virtual image of the reproduced holographicimage is viewed closer to the viewer and the distance D is reduced.Also, as the location value of the holographic plane increases in thenegative (−) direction, that is, the holographic plane is moved awayfrom the reflective surface of the spatial light modulator 130 in adirection opposite to the direction in which light travels, the virtualimage of the reproduced holographic image is viewed at a distance fromthe viewer and the distance D is increased.

FIG. 8 is a block diagram of a configuration of a multi-image displayapparatus 200 according to an example embodiment. Referring to FIG. 8,the multi-image display apparatus 200 may include a left eye lightsource 110L, a left eye optical system 120L, a left eye spatial lightmodulator 130L, a right eye light source 110R, a right eye opticalsystem 120R, and a right eye spatial light modulator 130R. Theconfigurations of the left eye optical system 120L and the right eyeoptical system 120R may be the same as the configuration of the opticalsystem 120 described with reference to FIGS. 1 through 4. The opticalcomponents in the left eye optical system 120L may be disposed in anopposite direction to the optical components in the right eye opticalsystem 120R, that is, symmetrically disposed.

Also, the configurations of the left eye light source 110L and the righteye light source 110R may be the same as the configuration of the lightsource 110 described with reference to FIGS. 1 through 4, and theconfigurations of the left eye spatial light modulator 130L and theright eye spatial light modulator 130R may be the same as theconfiguration of the spatial light modulator 130 described withreference to FIGS. 1 through 4. The left eye spatial light modulator130L and the right eye spatial light modulator 130R may reproduceholographic images of different viewpoints according to the control ofan image processing apparatus. For example, the left eye spatial lightmodulator 130L may reproduce a holographic image having a left eyeviewpoint of a viewer, and the right eye spatial light modulator 130Rmay reproduce a holographic image having a right eye viewpoint of theviewer. The multi-image display apparatus 200 may provide a virtualholographic image together with an image including an actual externalscene in both eyes of a viewer.

The configuration of the optical system 120 described with reference toFIGS. 1 through 4 may be modified in various ways as needed. Forexample, the order of some optical elements in the optical system 120described with reference to FIGS. 1 through 4 may be changed asnecessary. Also, in a light path between the light source 110 and an eyeE of a viewer, the polarization state of light may be differentlyselected from the polarization state described with reference to FIGS. 1through 4 by differently selecting the characteristics of polarizationdependent components or by arranging additional polarization selectivecomponents. Also, an optical path may further be bent by additionallyarranging a mirror on the optical path between the light source 110 andthe viewer's eye E.

FIG. 9 is a diagram illustrating an arrangement of some components of amulti-image display apparatus according to an example embodiment. FIG. 9shows the multi-image display apparatus downwardly viewed from the top,and some configurations are shown in cross-section shapes. In theexample embodiment described above with reference to FIG. 4, the lightsource 110 is disposed on an upper surface of the first beam splitter121 in a +z direction, but the location of the light source 110 is notlimited thereto. As depicted in FIG. 9, the light source 110 may bedisposed on a side surface of the first beam splitter 121 in a −xdirection. In this case, the first beam splitter 121 depicted in FIG. 9is rotated by 90 degrees with respect to an optical axis when comparedwith the first beam splitter 121 depicted in FIG. 4. Then, the firstbeam splitter 121 may reflect light of a second linearly polarized lightcomponent incident on a side surface thereof in a direction towards thespatial light modulator 130. Also, the first beam splitter 121 maytransmit light of a first linearly polarized light component reflectedby the spatial light modulator 130.

In the example embodiment depicted in FIG. 9, the optical configurationafter the second beam splitter 124 may be the same as the embodimentdepicted in FIG. 4. The second beam splitter 124 reflects light havingthe first linearly polarized light component and transmits light havingthe second linearly polarized light component. Accordingly, a half-waveplate 125 c may further be disposed in front of the second beam splitter124. In FIG. 9, it is depicted that the half-wave plate 125 c isdisposed between the second lens 122 b and the second beam splitter 124,but the half-wave plate 125 c may be disposed on an optical path betweenthe first beam splitter 121 and the second beam splitter 124. Light ofthe first linearly polarized light component transmitted through thefirst beam splitter 121 is converted into light of the second linearlypolarized light component while passing through the half-wave plate 125c. Afterwards, the light of the second linearly polarized lightcomponent is transmitted through the second beam splitter 124 and isincident on the first mirror 126.

Instead, the light source 110 may be disposed on a lower surface of thefirst beam splitter 121 in a −z direction. In this case, the lightsource 110 and the third lens 127 (refer to FIG. 2) may be disposed onthe same side with respect to the optical axis of the optical system.Also, the first beam splitter 121 is rotated by 180 degrees with theoptical axis as a rotation axis when compared with the first beamsplitter 110 depicted in FIG. 4, and may reflect light of the firstlinearly polarized light component incident on a lower surface thereofin a direction towards the spatial light modulator 130.

FIG. 10 is a cross-sectional view illustrating an arrangement of somecomponents of a multi-image display apparatus according to an exampleembodiment. In FIG. 10, the multi-image display apparatus is depicted inthe same direction as the direction of the multi-image display apparatusof FIG. 3. In the example embodiment of FIG. 3, it is explained that thethird beam splitter 128 reflects the light of the first linearlypolarized light component and transmits the light of the second linearlypolarized light component. However, embodiments are not limited thereto.In the example embodiment depicted in FIG. 10, the third beam splitter128 a may be configured to transmit light of a first linearly polarizedlight component and reflect light of a second linear polarized lightcomponent. In the example embodiment depicted in FIG. 10, the remainingconfiguration of the optical system except for the third beam splitter128 a may be the same as the optical system 120 depicted in FIGS. 2 and3. In this case, the second quarter-wave plate 125 b and the secondmirror 129 may be disposed on a lower side of the third beam splitter128 a in a −z direction.

Then, light of the first linearly polarized light component reflected bythe second beam splitter 124 and passed through the third lens 127 istransmitted through the third beam splitter 128 a and the secondquarter-wave plate 125 b and enters the second mirror 129. At this time,the light has a first circularly polarized light component. Light havingthe first circularly polarized light component is reflected in anopposite direction by the second mirror 129 and is converted into asecond circularly polarized light component. Then, the light may have asecond linearly polarized light component by passing through the secondquarter-wave plate 125 b again. Light having the second linearlypolarized light component is reflected by the third beam splitter 128 aand enters the eye E of the viewer.

Of light including an external scene, light having the first linearlypolarized light may enter the viewer's eye E through the third beamsplitter 128 a. Accordingly, a holographic image IMG1 includes a secondlinearly polarized light component and an external image IMG2 includes afirst linearly polarized light component. In the example embodimentdepicted in FIG. 3, both the holographic image IMG1 and the externalimage IMG2 have a second linearly polarized light component.

According to example embodiments, the first mirror 126 and the secondmirror 129 may be concave mirrors having positive (+) refractive power.However, embodiments are not limited thereto, and either or both of thefirst mirror 126 and the second mirror 129 may be a plane mirror. Forexample, FIG. 11 is a cross-sectional view illustrating an arrangementof some components of a multi-image display apparatus according to anexample embodiment. In FIG. 11, the multi-image display apparatus isdepicted in the same direction as the direction of the multi-imagedisplay apparatus of FIG. 2. Referring to FIG. 11, the first mirror 126of the multiple image display apparatus may be a plane mirror. When thefirst mirror 126 is a plane mirror, the curvatures of the first lens 122a, the second lens 122 b, and the third lens 127 and the second mirror129 may be controlled so that a holographic image is more accuratelyprovided to the viewer's eye E.

Also, FIG. 12 is a cross-sectional view illustrating an arrangement ofsome components of a multi-image display apparatus according to anexample embodiment. In FIG. 12, the multi-image display apparatus isdepicted in the same direction as the direction of the multi-imagedisplay apparatus of FIG. 3. Referring to FIG. 12, the second mirror 129of the multiple image display apparatus may be a plane mirror. When thesecond mirror 129 is a plane mirror, the curvatures of the first lens122 a, the second lens 122 b, and the third lens 127 and the firstmirror 126 may be controlled so that a holographic image is moreaccurately provided to the viewer's eye E. Instead, both the firstmirror 126 and the second mirror 129 may be plane mirrors. In this case,a holographic image may be more accurately provided to the viewer's eyeE by controlling the curvatures of the first lens 122 a, the second lens122 b, and the third lens 127.

FIG. 13 is a cross-sectional view illustrating an arrangement of somecomponents of a multi-image display apparatus according to an exampleembodiment. Referring to FIG. 13, the multi-image display apparatus mayinclude a light source 110 that provides parallel light to the firstbeam splitter 121. For example, the light source 110 may include a beamcombiner 111 facing the first beam splitter 121, a first light-emittingdevice 112G disposed to face the first surface 111 a of the beamcombiner 111, a first collimating lens 113G between the beam combiner111 and the first light-emitting device 112G, a second light-emittingdevice 112R facing a second surface 112 b of the beam combiner 111, asecond collimating lens 113R between the beam combiner 111 and thesecond light-emitting device 112R, a third light-emitting device 1128facing a third surface 111 c of the beam combiner 111, and a thirdcollimating lens 1138 between the beam combiner 111 and the thirdlight-emitting device 112B. The beam combiner 111 may be disposed sothat a fourth surface 111 d thereof faces the first beam splitter 121.For example, the beam combiner 111 may be an X-cube.

In a configuration of the light source 110, light emitted from the firstlight-emitting device 112G is converted to parallel light by the firstcollimating lens 113G, is reflected by the beam combiner 111, and mayenter the first beam splitter 121. Light emitted from the secondlight-emitting device 112R is converted to parallel light by the secondcollimating lens 113R and may enter the first beam splitter 121 throughthe beam combiner 111. Light emitted from the third light-emittingdevice 1128 is converted to parallel light by the third collimating lens1138, is reflected by the beam combiner 111, and may enter the firstbeam splitter 121.

According to example embodiments, the spatial light modulator 130 may bea reflective spatial light modulator that modulates incident light whilereflecting it. However, embodiments are not limited thereto, and thespatial light modulator 130 may be a transmissive spatial lightmodulator that modulates incident light while transmitting the incidentlight. For example, FIG. 14 is a cross-sectional view illustrating anarrangement of some components of a multi-image display apparatusaccording to an example embodiment, and the multi-image displayapparatus is depicted in the same direction as the direction of themulti-image display apparatus of FIG. 2.

Referring to FIG. 14, the multiple image display apparatus may include asurface light source 110 a that emits parallel light and a transmissivespatial light modulator 130 a instead of the light source 110, the firstbeam splitter 121, and the spatial light modulator 130 of reflectivetype depicted in FIG. 2. Accordingly, the surface light source 110 a,the transmissive spatial light modulator 130 a, and the first lens 122 amay be sequentially disposed in a traveling direction of light. Theconfiguration after the first lens 122 a may be the same as theconfiguration described with reference to FIG. 2 and FIG. 3. In thiscase, the second beam splitter 124 may be configured to transmit lightincident from the transmissive spatial light modulator 130 a. Theoptical system may include a first optical path from the surface lightsource 110 a to the first mirror 126, a second optical path in avertical direction between the second beam splitter 124 and the thirdbeam splitter 128 (refer to FIG. 3), and a third light path from thesecond mirror 129 (refer to FIG. 3) and the viewer.

Meanwhile, the multi-image display apparatus may include a point lightsource and a collimating lens instead of the surface light source 110 a.The transmissive spatial light modulator 130 a may include, for example,a semiconductor modulator based on a compound semiconductor, such asgallium arsenide (GaAs), or a liquid crystal device (LCD). When thetransmissive spatial light modulator 130 a is used, the first beamsplitter 121 may be omitted, and thus, the configuration of the opticalsystem may be more simplified.

FIG. 15 is a perspective view illustrating a configuration of amulti-image display apparatus 300 according to an example embodiment.Referring to FIG. 15, the multi-image display apparatus 300 may includea light source 310, an optical system 320, and a spatial light modulator330. The light source 310 may be the same as the light source 110 of themulti-image display apparatus 100 depicted in FIG. 1, and the spatiallight modulator 330 may be the same as the spatial light modulator 130of the multi-image display apparatus 100 depicted in FIG. 1.

The optical system 320 may include a first lens 322 a, a first beamsplitter 321, a spatial filter 323, a second lens 322 b, a half-waveplate 326, and a first mirror 324 that are sequentially disposed in the+y direction. Also, the optical system 320 may further include a thirdlens 327 and a second beam splitter 328 that are sequentially disposedin the −z direction below the first mirror 324. The optical system 320may further include a quarter-wave plate 325 and a second mirror 329that are disposed in the −x direction facing the second beam splitter328. Accordingly, when the optical system 320 is compared with theoptical system 120 of the multi-image display apparatus 100 depicted inFIG. 1, the optical system 320 of the multi-image display apparatus 300includes the first mirror 324 instead of the second beam splitter 124and does not include the first quarter-wave plate 125 a and the firstmirror 126 but further includes the half-wave plate 326.

FIG. 16 is a cross-sectional view taken along a direction illustratingan arrangement of some of the components of the multi-image displayapparatus 300 of FIG. 15. For example, FIG. 16 is a cross-sectional viewof the optical system 320 cut in a plane including a z-axis and a y-axisto show the components from the spatial light modulator 330 to the thirdlens 327 disposed in the +y direction.

Referring to FIG. 16, the light source 310 is disposed facing a firstsurface 321 a of the first beam splitter 321. Accordingly, light emittedfrom the light source 310 is incident on the first surface 321 a of thefirst beam splitter 321. The first beam splitter 321 is a polarizationbeam splitter that reflects light having a first linearly polarizedlight component and transmits light having a second linearly polarizedlight component orthogonal to the first linearly polarized lightcomponent. Light having the first linearly polarized light component ofthe light emitted from the light source 310 is reflected by the firstbeam splitter 321 and light having the second linearly polarized lightcomponent may be transmitted through the first beam splitter 321.

The spatial light modulator 330 is disposed facing a second surface 321b of the first beam splitter 321. The light having the first linearlypolarized light component reflected from the first beam splitter 321 isemitted through the second surface 321 b of the first beam splitter 321and enters the spatial light modulator 330. The first lens 322 aconverts light coming from the first beam splitter 321 into parallellight having a constant beam diameter. The spatial light modulator 330modulates and reflects incident light, and the modulated lightinterferes with each other to form a holographic image. Then, when thelight is modulated by the spatial light modulator 330, the light isrotated 90 degrees and the light has the second linearly polarized lightcomponent. The light including the holographic image is incident againon the second surface 321 b of the first beam splitter 321. At thistime, the light is focused through the first lens 322 a. The lighthaving the second linearly polarized light component is transmittedthrough the first beam splitter 321 and may be emitted through the thirdsurface 321 c of the first beam splitter 321 facing the second surface321 b.

The light transmitted through the first beam splitter 321 enters thefirst mirror 324 after passing through the spatial filter 323, thesecond lens 322 b, and the half-wave plate 326. In FIG. 16, it isdepicted that the spatial filter 123, the second lens 122 b, and thehalf-wave plate 326 are sequentially disposed in a traveling directionof the light, but embodiments are not limited thereto. For example, thespatial filter 123 and the second lens 122 b may be disposed on anoptical path between the first beam splitter 321 and the first mirror324 regardless of the order. Also, the half-wave plate 326 may bedisposed on any location on the optical path between the first beamsplitter 321 and the second beam splitter 328.

The light having the second linearly polarized light component may havea first linearly polarized light component while a phase thereof ischanged 180 degrees by the half-wave plate 326. The light having thefirst linearly polarized light component is reflected by the firstmirror 324 and is incident on the third lens 327 located below the firstmirror 324. Accordingly, the traveling direction of light is bent byabout 90 degrees by the first mirror 324. For this purpose, the firstmirror 324 may be disposed at an angle with respect to the half-waveplate 326 to change the traveling direction of the light by about 90degrees. Then, the light reflected by the first mirror 324 travels inthe −z direction. Also, in FIG. 16, the first mirror 324 is a simpleplane mirror, but embodiments are not limited thereto. For example, thefirst mirror 324 may be a concave mirror having a concave reflectivesurface to enlarge an image.

The light reflected by the first mirror 324 passes through the thirdlens 327 and enters the second beam splitter 328. The light incident onthe second beam splitter 328 has a first linearly polarized lightcomponent. The configuration and operation of the second beam splitter328, the quarter-wave plate 325, and the second mirror 329 may be thesame as those of the third beam splitter 128, the second quarter-waveplate 125 b, and the second mirror 129 described with reference to FIG.3. For example, the second beam splitter 328 may be a polarization beamsplitter that reflects light having a first linearly polarized lightcomponent and transmits light having a second linearly polarized lightcomponent orthogonal to the first linearly polarized light component.The configuration and operation of the second beam splitter 328, thequarter-wave plate 325, and the second mirror 329 may be the same asthose of the third beam splitter 128, the second quarter-wave plate 125b, and the second mirror 129 described with reference to FIG. 10. Inthis case, the second beam splitter 328 may be configured to transmitlight of the first linearly polarized light component and reflect lightof the second linear polarized light component. Accordingly, the secondbeam splitter 328 transmits the light reflected from the first mirror324 and reflects the light reflected from the second mirror 329.

FIG. 17 is a cross-sectional view taken along a direction illustratingan arrangement of some of the components of the multi-image displayapparatus 300 shown in FIG. 15. When compared with the arrangement ofFIG. 16, the half wave-plate 326 is omitted from the arrangement of FIG.17. In this case, the light reflected by the first mirror 324 and entersthe second beam splitter 328 has a second linearly polarized lightcomponent.

FIG. 18 is a cross-sectional view taken along another directionillustrating an arrangement of some other components of the multi-imagedisplay apparatus of FIG. 15. For example, FIG. 18 is a cross-sectionalview of the optical system 320 taken along a plane including the z-axisand the x-axis in FIG. 15 so as to specifically show the path of lightfrom the first mirror 324 to the viewer's eye. Since the sectional viewof FIG. 18 is rotated by 90 degrees with respect to the sectional viewof FIG. 17, in FIG. 18, the linearly polarized light component isdisplayed in reverse to FIG. 17. For example, although the firstlinearly polarized light component is represented by ‘

’ and the second linearly polarized light component is represented by ‘

’ and ‘↔’ in FIG. 17, but in FIG. 18, the first linearly polarized lightcomponent is represented by ‘

’ and the second linearly polarized light component is represented by ‘

’.

Referring to FIG. 18, the second beam splitter 328 may be a polarizationbeam splitter that reflects light having a second linearly polarizedlight component and transmits light having a first linearly polarizedlight component. Accordingly, the light of the second linearly polarizedlight component reflected by the first mirror 324 and incident on thesecond beam splitter 328 is reflected by the second beam splitter 328.At this time, a light path is bent by about 90 degrees, and the lighttravels in the −x direction. The light reflected by the second beamsplitter 328 passes through the quarter-wave plate 325 and enters thesecond mirror 329. The light incident on the second mirror 329 has thesecond circularly polarized light component by the quarter-wave plate325.

The light having the second circularly polarized light component isreflected by the second mirror 329 in an opposite direction, that is, ina direction of 180 degrees with respect to an incidence direction.Accordingly, the light reflected by the second mirror 329 travels in the+x direction. At this time, the polarized light component of the lightreflected by the second mirror 329 is converted into a first circularlypolarized light component. Then, the light again has a first linearlypolarized light component while passing through the quarter-wave plate325. Then, the light having the first linearly polarized light componentis transmitted through the second beam splitter 328 and enters the eye Eof the viewer. The second mirror 329 may be a concave mirror having aconcave reflective surface to enlarge the image or may be a simple planemirror.

The second beam splitter 328 may be a polarization beam splitter thatreflects light having a first linearly polarized light component andtransmits light having a second linearly polarized light component. Inthis case, the configuration and operation of the second beam splitter328, the quarter-wave plate 325, and the second mirror 329 are the sameas those of the third beam splitter 128, the second quarter-wave plate125 b, and the second mirror 129, and only a polarization direction maybe reversed.

FIGS. 19 through 21 illustrate various electronic devices employing themulti-image display apparatus 100 according to the example embodimentsdescribed above. As depicted in FIGS. 19 to 21, the multi-image displayapparatus 100 may constitute a wearable device. The multi-image displayapparatus 100 may be applied to a wearable device. For example, themulti-image display apparatus 100 may be applied to a head mounteddisplay (HMD). Also, the multi-image display apparatus 100 may beapplied to a glasses-type display, a goggle-type display, etc. Thewearable electronic devices shown in FIGS. 19 through 21 may be operatedin interconnection with a smart phone. The multi-image display apparatus100 may be a VR display device, an AR display device, or a MR displaydevice of a head-mounted type or a glasses or goggle type capable ofproviding a virtual reality or providing a virtual image together withan external real image.

Also, the multi-image display apparatus 100 may be included in a smartphone, and the smart phone itself may be used as a multi-image displayapparatus. In other words, the multi-image display apparatus 100 may beapplied to a small electronic device such as a mobile electronic deviceother than the wearable device as shown in FIGS. 19 through 21. However,embodiments are not limited thereto, and the application field of themulti-image display apparatus 100 may be variously changed. For example,the multi-image display apparatus 100 may be applied not only to realizea VR, an AR, or a MR, but also to other fields. For example, themulti-image display apparatus 100 may be applied to a small televisionor a small monitor that may be worn by a user.

While one or more example embodiments have been described with referenceto the figures, it will be understood by those of ordinary skill in theart that various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A multi-image display apparatus comprising: alight source configured to emit light; a spatial light modulatorconfigured to provide a first image by modulating the light emitted fromthe light source; and an optical system configured to transmit the firstimage provided by the spatial light modulator to a viewer, wherein theoptical system is configured such that a first travelling path of thefirst image provided by the spatial light modulator comprises a firstoptical path in a first direction, a second optical path in a seconddirection orthogonal to the first direction, and a third optical path ina third direction orthogonal to the first direction and the seconddirection, and wherein the optical system is configured such that thefirst image and a second image provided from a second travelling pathdifferent from the first travelling path are provided to the vieweralong the third optical path.
 2. The multi-image display apparatus ofclaim 1, wherein the first image is a virtual holographic image and thesecond image is an external image comprising an actual external scene.3. The multi-image display apparatus of claim 1, wherein the spatiallight modulator comprises a reflective spatial light modulatorconfigured to reflect and modulate the light emitted from the lightsource.
 4. The multi-image display apparatus of claim 3, wherein theoptical system comprises: a first beam splitter configured to reflectthe light emitted from the light source to the spatial light modulatorand transmit light reflected by the spatial light modulator; a secondbeam splitter configured to transmit the light transmitted from thefirst beam splitter; a first mirror configured to reflect the lighttransmitted through the second beam splitter towards the second beamsplitter; a third beam splitter provided in the second direction fromthe second beam splitter; and a second mirror configured to reflectlight reflected from the third beam splitter towards the third beamsplitter.
 5. The multi-image display apparatus of claim 4, wherein thesecond beam splitter is configured to reflect the light reflected fromthe first mirror towards the third beam splitter.
 6. The multi-imagedisplay apparatus of claim 4, wherein each of the first beam splitter,the second beam splitter, and the third beam splitter comprises asemi-transmissive mirror configured to reflect a first half of anincident light and transmit a second half of the incident light.
 7. Themulti-image display apparatus of claim 4, wherein each of the first beamsplitter, the second beam splitter, and the third beam splittercomprises a polarization beam splitter configured to reflect lighthaving a first linearly polarized light component and transmit lighthaving a second linearly polarized light component that is orthogonal tothe first linearly polarized light component.
 8. The multi-image displayapparatus of claim 7, wherein the optical system further comprises afirst quarter-wave plate provided between the second beam splitter andthe first mirror, and a second quarter-wave plate provided between thethird beam splitter and the second mirror.
 9. The multi-image displayapparatus of claim 7, wherein the third beam splitter is configured toreflect the light transmitted from the second beam splitter and transmitthe light reflected from the second mirror.
 10. The multi-image displayapparatus of claim 9, wherein the second mirror comprises a firstsurface facing the third beam splitter and a second surface opposite tothe first surface, and wherein the second mirror is configured toreflect a first image incident on the first surface and to transmit asecond image incident on the second surface.
 11. The multi-image displayapparatus of claim 4, wherein each of the first beam splitter and thesecond beam splitter comprises a polarization beam splitter configuredto reflect light having a first linearly polarized light component andtransmit light having a second linearly polarized light component thatis orthogonal to the first linearly polarized light component, andwherein the third beam splitter comprises a polarization beam splitterconfigured to transmit light having the first linearly polarized lightcomponent and reflect light having the second linearly polarized lightcomponent orthogonal to the first linearly polarized light component.12. The multi-image display apparatus of claim 11, wherein the thirdbeam splitter is configured to transmit the light from the second beamsplitter and to reflect the light reflected from the second mirror. 13.The multi-image display apparatus of claim 4, wherein the optical systemfurther comprises: a first lens provided between the spatial lightmodulator and the first beam splitter; a second lens provided betweenthe first beam splitter and the second beam splitter; and a third lensprovided between the second beam splitter and the third beam splitter.14. The multi-image display apparatus of claim 13, wherein each of thefirst lens and the second lens comprises a convex lens, and the thirdlens comprises a concave lens.
 15. The multi-image display apparatus ofclaim 13, wherein the optical system further comprises a spatial filterprovided between the first beam splitter and the second beam splitterproximate to a focal point of the first lens.
 16. The multi-imagedisplay apparatus of claim 4, wherein the first optical path is providedbetween the spatial light modulator and the first mirror, the secondoptical path is provided between the second beam splitter and the thirdbeam splitter, and the third optical path is provided between the secondmirror and the viewer.
 17. The multi-image display apparatus of claim16, wherein the first optical path and the third optical path havedifferent positions in the second direction, and the second optical pathis vertically provided between the first optical path and the thirdoptical path in the second direction.
 18. The multi-image displayapparatus of claim 4, wherein at least one of the first mirror and thesecond mirror comprises a concave mirror.
 19. The multi-image displayapparatus of claim 4, wherein the second mirror comprises a concavemirror, and wherein the optical system is configured to form a realimage of the first image between a focal point of the second mirror andthe second mirror.
 20. The multi-image display apparatus of claim 4,wherein at least one of the first mirror and the second mirror comprisesa concave mirror.
 21. The multi-image display apparatus of claim 3,wherein the optical system comprises: a first beam splitter configuredto reflect the light emitted from the light source towards the spatiallight modulator and to transmit the light reflected from the spatiallight modulator; a first mirror configured to reflect the lighttransmitted from the first beam splitter; a second beam splitterprovided in the second direction from the first mirror in the seconddirection; and a second mirror configured to reflect light reflectedfrom the second beam splitter towards the second beam splitter.
 22. Themulti-image display apparatus of claim 21, wherein the second beamsplitter is configured to reflect the light from the first mirror and totransmit the light reflected from the second mirror.
 23. The multi-imagedisplay apparatus of claim 22, wherein each of the first beam splitterand the second beam splitter comprises a polarization beam splitterconfigured to reflect light having a first linearly polarized lightcomponent and to transmit light having a second linearly polarized lightcomponent that is orthogonal to the first linearly polarized lightcomponent, and wherein the optical system further comprises a half-waveplate provided between the first beam splitter and the second beamsplitter, and a quarter-wave plate provided between the second beamsplitter and the second mirror.
 24. The multi-image display apparatus ofclaim 22, wherein the first beam splitter comprises a polarization beamsplitter configured to reflect light having a first linearly polarizedlight component and to transmit light having a second linearly polarizedlight component that is orthogonal to the first linearly polarized lightcomponent, and wherein the second beam splitter comprises a polarizationbeam splitter configured to transmit light having the first linearlypolarized light component and to reflect light having the secondlinearly polarized light component, and wherein the optical systemfurther comprises a quarter-wave plate provided between the second beamsplitter and the second mirror.
 25. The multi-image display apparatus ofclaim 21, wherein the second beam splitter is configured to transmitlight from the first mirror and to reflect light reflected from thesecond mirror.
 26. The multi-image display apparatus of claim 1, whereinthe spatial light modulator comprises a transmissive spatial lightmodulator configured to transmit and modulate the light emitted from thelight source.
 27. The multi-image display apparatus of claim 26, whereinthe optical system comprises: a second beam splitter configured totransmit the light provided from the spatial light modulator; a firstmirror configured to reflect the light transmitted through the secondbeam splitter towards the second beam splitter; a third beam splitterprovided in the second direction from the second beam splitter; and asecond mirror configured to reflect the light from the third beamsplitter towards the third beam splitter.
 28. The multi-image displayapparatus of claim 27, wherein the optical system further comprises: afirst lens and a second lens provided between the spatial lightmodulator and the second beam splitter; a spatial filter providedbetween the first lens and the second lens; and a third lens providedbetween the second beam splitter and the third beam splitter.
 29. Themulti-image display apparatus of claim 28, wherein each of the firstlens and the second lens comprises a convex lens, and the third lenscomprises a concave lens.
 30. The multi-image display apparatus of claim27, wherein the first optical path is provided between the light sourceand the first mirror, the second optical path is provided between thesecond beam splitter and the third beam splitter, and the third opticalpath is provided between the second mirror and the viewer.